The Shope papilloma-carcinoma system has great potential in the definition of basic phenomena associated with the neoplastic process. This is true since, in the domestic rabbit there is a viral induced progression from normal skin to papillomas to carcinomas. The viral genome is conserved in all neoplasms, but virus is not made. We propose to qualitatively and quantitatively determine the extent to which viral gene products are present in the two neoplasms. This beginning effort should ultimately lead to a definition of the precise role of the virus and its gene products in induction and maintenance of benign and malignant neoplasms.